Sensors used in process control systems for measuring basis or area weight of a web of paper need to develop accurate measurement information for a quickly moving, fluttering web, while operating in a high humidity, dirty, hot and/or wet environment. These sensors are usually mounted on measurement platforms that scan the sensors slowly in a cross-process direction as the process web (web of paper) moves relatively rapidly in a process direction. Although beta instruments (or beta gauges) are relatively insensitive to the atomic composition of the measured material, they have enough composition sensitivity to cause correlation errors when used to measure paper basis weight in the presence of varying amounts of additives like clay, chalk or titanium dioxide, TiO2. Beta instrument suppliers have developed methods to reduce the composition sensitivity of the beta instruments, generally using a nuclear diffuser or backscatter generator. However, as the beta instrument is made more insensitive to composition, the signal to noise ratio is reduced.
Accordingly, there is a need for a system and method that provides on-line compensation of a beta gauge for atomic composition changes in a web being manufactured, for example a paper web, without substantial reduction in signal to noise ratio.